The present application relates to a thin-film transistor (TFT) using an oxide semiconductor, a method of manufacturing the same, and a display unit as well as an electronic apparatus each having the thin-film transistor.
In recent years, with increases in size and definition of displays, there has been demand for high mobility in TFTs of drive devices. Therefore, there have been actively developed TFTs using oxide semiconductors such as zinc (Zn) oxide, indium (In) oxide, gallium (Ga) oxide, tin (Sn) oxide, aluminum (Al) oxide, titanium (Ti) oxide, and a mixture of any of these oxides. It has been found that TFTs using complex oxides of Zn, In, and Ga, in particular, have large electron mobility and exhibit excellent electrical properties, as compared with TFTs using amorphous silicon (a-Si:H) usually employed in liquid crystal displays, etc.
Among such TFTs using oxide semiconductors, those having a bottom-gate type structure and those having a top-gate type structure have been reported so far. In the bottom-gate type structure, a thin-film layer made of an oxide semiconductor is provided on a gate electrode, with a gate insulating film interposed therebetween. This structure is similar to a currently-commercialized TFT structure in which amorphous silicon is used as a channel. For this reason, a manufacturing process of the currently-available TFT employing amorphous silicon is readily used for the TFTs having the bottom-gate type structure. Thus, the bottom-gate type structure is often employed in the TFTs using oxide semiconductors.
In addition, for improvement of the reliability of the oxide semiconductor TFTs, it has been proposed to form a protective film made of Al2O3 or the like on a drain electrode and a source electrode made of aluminum, molybdenum, ITO, and the like (for example, see Toshiaki Arai et al., SID 10 Digest (2010), and Japanese Unexamined Patent Application Publication Nos. 2011-187506 and 2012-4371).
It can be said that the oxide semiconductor has characteristics in which contact between a semiconductor film and a transparent oxide electrode is possible because the channel itself is an oxide. Therefore, a completely transparent display can be expected to be realized. In a transparent display, not only TFTs but also flattening films as well as electrodes are made transparent so that high transmittance is achieved. Meanwhile, light emitted as backlight from EL devices and the like directly enters the TFTs, because each layer is transparent as described above. In particular, when the wavelength of the incident light is in the range of ultraviolet light, operation of an oxide semiconductor device is destabilized. For this reason, in order to realize a highly reliable transparent display, it is necessary to block the above-described light incident upon the TFTs. In this regard, it has been proposed to provide a light-shielding film, for example, by forming a flattening film on a source electrode and a drain electrode, and then forming an electrode thereon (for example, see C. S. Chuang et al., SID 08 Digest (2008)).
Further, it has been proposed that, when a transparent conductive film is used as a wiring of an active matrix display, a low-resistance wiring in which a main part of the above-mentioned wiring is made of Al or the like is routed for the purpose of reducing wiring resistance (for example, see Japanese Unexamined Patent Application Publication No. 2010-98280).